Commercial Total Organic Carbon (TOC) analyzers are used to measure the quantity of organic carbon present in a water sample, which is an indicator of water purity. Applications for TOC measurements include ultrapure water for pharmaceutical and electronics manufacturing, as well as Municipal drinking water and wastewater and Industrial wastewater from chemical and petrochemical plants, as examples.
Measurement of TOC relies on the conversion or oxidation of organic material in a water sample to CO2, which can then be measured by conductivity or Nondispersive Infrared (NDIR) detection, as examples. Two common methods of oxidation include UV/Persulfate and high-temperature combustion. The UV/Persulfate method uses the combination of ultraviolet light and strong chemical oxidants, for example, sodium persulfate, to convert organic material to CO2. High-temperature combustion uses thermal oxidation processes, often in the presence of catalysts, to convert the organic materials to CO2. Both methods use an acid, for example, phosphoric acid, to initially remove “Total Inorganic Carbon” or TIC present in the water sample, as CO2, prior to the oxidation of the organic carbon. An example of a commercially available UV/Persulfate TOC analyzer is the GE/Sievers 900 Laboratory Analyzer, and an example of a high temperature combustion TOC analyzer is the Shimadzu TOC-L.
Chemical oxidants, acids, and dilution water are “reagents” consumed during TOC analyses, and can be expensive and difficult to handle for users of UV/Persulfate TOC analyzers. These reagents are purchased or prepared in separate containers at concentrations required by the manufacturers of TOC analysis equipment. In addition, currently available UV/Persulfate TOC analyzers require separate steps for the analysis, with each step designed to use one of the reagents. For example, the sample to be analyzed is often first diluted using added water to ensure that the sample TOC or TIC falls within the measurement range of the NDIR detector. Some commercial analyzers employ an “Auto-ranging” feature that automatically injects the correct dilution volume based on a preliminary measurement of the sample. An acid reagent is first added to react with the inorganic carbon compound in the sample to generate CO2, followed by sparging the solution with a carbon dioxide free carrier gas, for example, purified oxygen or nitrogen, to remove the generated CO2, which may be measured as TIC, or simply discarded. A chemical oxidant is then added to oxidize the organic carbon present in the sample to CO2, generally with the aid of ultraviolet radiation. The CO2 is again sparged from the solution using a carbon dioxide free gas, and measured yielding the Total Organic Carbon” or TOC. The sum of the TIC and TOC yields the Total Carbon, or TC, in the sample. Collectively, reagent preparation and/or handling along with these analysis steps comprise the reagent “workflow” required to measure TOC in a UV/Persulfate analyzer.